The long-term objective of this work is to understand the genetic origin(s) and biologic function(s) of unique tumor antigens recognized by CD4+ T cells. The immediate goals of this work are to determine whether these antigens are usually caused by somatic mutation (and thus are truly tumor-specific), whether they commonly involve ribosomal proteins, and whether they are important in the malignant process, representing targets for T cell mediated regression (or progression) of cancer. The first Aim will be to determine whether certain principles about the molecular nature of the antigens can be established. In particular, it will be determined whether unique CD4+ T cell-recognized antigens are generated by somatic mutation and thus truly tumor-specific and whether ribosomal proteins are a common source of these antigens. A novel sensitive strategy that already has been used to identify a ribosomal tumor-specific antigen will be used. This strategy uses tumor-specific CD4+ T cell hybridomas to screen fractions derived from cell fractionation, RP-HPLC and SDS-PAGE, followed by micro-sequencing of the relevant slice of membrane identified by T cell Western. Whether UV-induced or spontaneous tumors elicit tumor-specific CD4+ T cell responses to ribosomal proteins will also be tested. T cell Western analysis of 2D gel blots will be used to identify the ribosomal proteins involved. The cDNA sequence of the implicated protein expressed by the tumor will be compared with that of autologous nonmalignant fibroblasts to localize the mutation and to determine if the antigen results from a somatic rather than a germline mutation and thus represents a truly tumor-specific antigen. The second Aim examines the functional role of the tumor-specific CD4+ T-cell recognized mutant L9 protein in malignancy. Thus, the investigator will determine whether expression of the mutant L9 gene results in the increased rate of growth of the progressor variant compared to the parental tumor in T-cell deficient mice. They will also determine whether the mutant L9 protein acts as an oncogene in standard assays or whether mutant L9 has immortalizing functions. The third Aim will use mutant L9 as a target to determine whether responses against this antigen can be preventive or even therapeutic, how naive mice respond to the mutant L9 when challenged with the tumor, and how such an immune response influences the regression or progression of the tumor. A better understanding of the molecular and functional nature of unique CD4+ T cell-recognized tumor antigens and their role in T cell mediated tumor regression/rejection may help in the development of novel strategies against cancer.